1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method of manufacturing the solid electrolytic capacitor, and particularly to a solid electrolytic capacitor having high heat resistance and a method of manufacturing the solid electrolytic capacitor.
2. Description of the Related Art
In recent years, electronic devices have been digitized and increased in frequency, which requires a compact and large-capacity solid electrolytic capacitor having a low impedance even in a high frequency region.
As a solid electrolytic capacitor satisfying the above-described requirement, a wound-type solid electrolytic capacitor has been developed. The wound-type solid electrolytic capacitor has a configuration in which a conductive polymer layer as a solid electrolyte is formed in a gap between an anode body and a cathode body which are wound with a separator interposed therebetween. The wound-type configuration as described above allows implementation of a compact and large-capacity solid electrolytic capacitor.
Furthermore, in the solid electrolytic capacitor, polymers such as polypyrrole and polythiophene having high conductivity is employed for a conductive polymer layer in order to implement a decreased impedance in a high frequency region. Among others, increasing attention is now being given to polyethylene dioxythiophene exhibiting a relatively slow reaction rate and excellent adhesiveness with the dielectric film of the surface of an anode body.
Various studies have been made in order to improve the performance as a conductive polymer layer made of this polyethylene dioxythiophene. For example, Japanese Patent Laying-Open No. 2001-176758 discloses that, in order to form polyethylene dioxythiophene with reduced variations in impedance, the blending amount of each component used as an oxidizer is prepared, and then, monomers are polymerized to form a conductive polymer layer.
Furthermore, Japanese Patent Laying-Open No. 2008-283136 discloses that, in order to improve the withstand voltage of the solid electrolytic capacitor, a polymerization retardant and an ionic solution containing cations and anions are used to form polyethylene dioxythiophene.
Meanwhile, in recent years, the reflow process is more likely to be performed by lead-free solder in consideration of the harmful effect of lead. The melting point of the lead-free solder is higher than that of the conventional lead solder, which results in a high temperature such as 200° C. to 270° C. during the reflow process using lead-free solder. The reflow process performed at such a high temperature causes a problem that the conductive polymer layer is deteriorated to cause a decrease in conductivity, leading to a decrease in the performance of the solid electrolytic capacitor.